The present invention relates to an electrode structure of an electro-optical device such as a liquid crystal display equipped with a color filter, or the like.
Several methods are known to accomplish color liquid crystal displays, color electro-optical devices, and the like. Among them, the most ordinary system is one that forms the color filter on one of the substrates because full color display is easy and television display can be made. A typical structure of a conventional color filter substrate is shown in FIGS. 2 and 3. In the drawings, reference numeral 1 represents a glass substrate, 2 is a color filter, 3 is an ITO film and 4 is a liquid crystal layer. The color filter 2 is formed by dying, electro deposition or printing. The ITO film 3 is formed by sputtering or vacuum deposition and is then patterned into an arbitrary shape.
FIG. 2 shows a structure wherein the ITO film 3 is formed on the color filter 2 and FIG. 3 shows a structure wherein the color filter 2 is formed on ITO 3. These structures have the following problems, respectively. In the structure shown in FIG. 2, inferior conduction is likely to occur at a step cover portion of the ITO film 3 relative to the color filter 2. Whereas the color filter 2 ordinarily consists of organic matter, the ITO film 3 consists of inorganic matter so that stress strain occurs due to thermal impact applied during the fabrication process of a panel and exerts adverse influences on the orientation of liquid crystal 4. This problem can be prevented by applying over-coating to the surface of the color filter 2 and then forming the ITO film 3 on the over-coating but this results in a complicated production process and in the increase of cost of production. On the other hand, the structure shown in FIG. 3 is free from the problem of inferior conduction of ITO but is not devoid of the problem in that a voltage applied practically to the liquid crystal layer 2 drops because the color filter 2 as the insulating material exists between the liquid crystal layer 4 and the ITO film 3 as the electrode for driving the liquid crystal.
To cope with this problem, attempts have been made to increase the dielectric constant of the color filter 2 or to render the color filter 2 itself conductive, but they have not yet been entirely practical.